Crankshafts typically employed in internal combustion engines utilize crankpin bearing surfaces, hereafter often called pins, offset with respect to the crankshaft axis and angularly disposed about the crank axis. In the manufacture of multiple pin crankshafts utilizing a plurality of crank pin bearing surfaces the pins are usually machined, as by turning, simultaneously. In conventional practice, a plurality of pin turning tools are connected to a pair of master cranks which rotate in synchronization with the workpiece wherein the tools move through an orbital motion equal to the motion of the workpiece pins. The tools are simultaneously brought into engagement with the workpiece pins and all of the pins are simultaneously machined. Such an operation requires a plurality of tool supports mounted upon the master cranks and the tool supports are mounted upon a carriage movable between tool engaging and retracted positions. Examples of such crankshaft machines are found in the assignee's U.S. Pat. Nos. 3,757,615 and 3,808,653.
Typical crankshaft lathes capable of machining all of the pins of a crankshaft simultaneously regardless of whether the crankshaft contains four, six or eight pins, are very expensive to manufacture, require expensive tooling, and each complete lathe is basically designed to machine a particular crankshaft, and major expenses and conversion procedures are required to tool a lathe to handle a different workpiece.
It is an object of the invention to provide a universal single spindle crankshaft lathe wherein a lathe is able to readily accommodate a variety of types of crankshaft workpieces. Thus, with a single lathe, crankshafts having two, four, six or eight pins may be readily accommodated with a minimum of tooling expense, and crankshaft prototype machining and short production runs can be economically processed at minimum costs.
A further object of the invention is to provide a universal crankshaft pin lathe wherein a single crankshaft pin is machined at a time and the machine automatically sequentially machines the workpiece pins in an accurate manner without operator attention.
An additional object of the invention is to provide a universal single spindle crankshaft lathe wherein the lathe employs a single drive motor to rotate both the workpiece and the tooling, and the relative rotational orientation between the crankshaft workpiece and tooling may be readily adjusted by automatic controls to accommodate the various crankshaft pins.
Yet another object of the invention is to provide a universal single spindle crankshaft lathe wherein the tools are mounted upon a compound carriage and slide permitting the tooling to be adjusted in a plane perpendicular to the crankshaft workpiece axis, and orbit in such a plane during machining, and also permit the tooling to be translated parallel to the workpiece axis for alignment with different workpiece pin bearings.
In the practice of the invention the lathe includes a base upon which headstock and tailstock spindles are mounted having chucks in which the workpiece crankshaft is mounted. A drive motor rotates both spindles through a first drive train. A carriage is mounted upon the base movable by an expansible chamber motor toward and away from the workpiece axis at right angles thereto. A slide mounted upon the carriage is adjustable in a direction parallel to the workpiece axis by an electric motor operating an anti-friction lead screw.
A tool case is mounted on the slide and supports a tool arm which includes cranks rotatably mounted thereon which are driven through a splined drive shaft whereby rotation of the drive shaft causes the tool arm, upon which the cutting tools are mounted, to orbit in a plane perpendicular to the workpiece axis. Thus, the movement of the tool arm permits the tools to follow the movement of the workpiece crankshaft pins during rotation and machine the pins to the accuracy desired.
The tool case is mounted upon the slide for movement parallel to the workpiece axis. Thus, the tool arm and tools are readily moved into a machining relationship to the workpiece pins, or retracted therefrom, and may also be shifted in an axial direction to be sequentially aligned with the pin that is to be machined.
The indexable connection between the drive for the headstocks and the drive shafts for the tool arm is shifted between drive and indexable positions by an expansible chamber motor. The tool arm drive shaft is adjusted between selective indexable positions by an index motor of the hydraulic type, and electric rotary switches sense the position of the tool arm drive to permit orientation of the tools to accommodate the particular pin to be machined. Preferably, orientation means are also associated with the head and tailstock spindle drive train such that the spindle drive will be oriented in a predetermined manner during adjustment of the indexable connection.
While the indexable connection may take a number of forms, in the preferred embodiment the connection consists of a female member having twelve recesses disposed about a shaft axis, and the male member includes three detents arranged at 120.degree. about a shaft axis selectively interfitting with the recesses whereby a positive drive between the headstock and tailstock spindles and tool arm drive shaft is maintained, and yet the relative rotational relationship therebetween may be readily adjusted to permit the machining of different workpiece pins.